Final answer:
The provided question regarding the year the National FFA Convention changed its delegate apportionment system to a fixed 475 cannot be answered with the provided references, but it is related to the concept of fair representation in democratic systems.
Step-by-step explanation:
The question provided does not include sufficient context to provide a specific year in which the delegates voted to change the delegate apportionment system at the National FFA Convention to a "fixed 475 system." However, by understanding the broader context of how delegates and representation have evolved in the United States, we can infer that this pertains to the process of democratic representation and the distribution of delegates, similar to how political parties distribute delegates for their national nominating conventions or how the Constitution originally established representation in Congress. Adjustments over time have been made to maintain fair representation, like the fixed number of House representatives established in 1929. Nevertheless, the specific details regarding the National FFA Convention are not included in the reference materials provided, and therefore, an accurate year for the change to a fixed 475 delegate system cannot be determined here.